From bec898a32669e63a7fbfa52b287c826722faaf4a Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Sat, 3 Mar 2018 11:47:14 +0000
Subject: [PATCH] Don't allow exceeding maximum MTU for a given platform

---
 src/yggdrasil/tun.go         | 11 +++++++++++
 src/yggdrasil/tun_darwin.go  |  8 +++++++-
 src/yggdrasil/tun_linux.go   |  8 +++++++-
 src/yggdrasil/tun_openbsd.go |  8 +++++++-
 src/yggdrasil/tun_other.go   |  8 +++++++-
 src/yggdrasil/tun_windows.go |  8 +++++++-
 6 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/src/yggdrasil/tun.go b/src/yggdrasil/tun.go
index b22a341..946467a 100644
--- a/src/yggdrasil/tun.go
+++ b/src/yggdrasil/tun.go
@@ -27,6 +27,17 @@ type tunDevice struct {
 	iface  tunInterface
 }
 
+type tunDefaultParameters struct {
+	maxMTU	int
+}
+
+func getMTUFromMax(mtu int) int {
+	if mtu > defaultTUNParameters().maxMTU {
+		return defaultTUNParameters().maxMTU
+	}
+	return mtu
+}
+
 func (tun *tunDevice) init(core *Core) {
 	tun.core = core
 	tun.icmpv6.init(tun)
diff --git a/src/yggdrasil/tun_darwin.go b/src/yggdrasil/tun_darwin.go
index eb1489f..98abc1b 100644
--- a/src/yggdrasil/tun_darwin.go
+++ b/src/yggdrasil/tun_darwin.go
@@ -10,6 +10,12 @@ import "golang.org/x/sys/unix"
 
 import water "github.com/neilalexander/water"
 
+func defaultTUNParameters() tunDefaultParameters {
+	return tunDefaultParameters{
+		maxMTU: 65535,
+	}
+}
+
 func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int) error {
 	if iftapmode {
 		tun.core.log.Printf("TAP mode is not supported on this platform, defaulting to TUN")
@@ -20,7 +26,7 @@ func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int)
 		panic(err)
 	}
 	tun.iface = iface
-	tun.mtu = mtu
+	tun.mtu = getMTUFromMax(mtu)
 	return tun.setupAddress(addr)
 }
 
diff --git a/src/yggdrasil/tun_linux.go b/src/yggdrasil/tun_linux.go
index 5fdf640..9287ff3 100644
--- a/src/yggdrasil/tun_linux.go
+++ b/src/yggdrasil/tun_linux.go
@@ -9,6 +9,12 @@ import "strings"
 
 import water "github.com/neilalexander/water"
 
+func defaultTUNParameters() tunDefaultParameters {
+	return tunDefaultParameters{
+		maxMTU: 65535,
+	}
+}
+
 func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int) error {
 	var config water.Config
 	if iftapmode {
@@ -24,7 +30,7 @@ func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int)
 		panic(err)
 	}
 	tun.iface = iface
-	tun.mtu = mtu //1280 // Lets default to the smallest thing allowed for now
+	tun.mtu = getMTUFromMax(mtu)
 	return tun.setupAddress(addr)
 }
 
diff --git a/src/yggdrasil/tun_openbsd.go b/src/yggdrasil/tun_openbsd.go
index c58518e..84ba2d9 100644
--- a/src/yggdrasil/tun_openbsd.go
+++ b/src/yggdrasil/tun_openbsd.go
@@ -15,6 +15,12 @@ import water "github.com/neilalexander/water"
 // to disable the PI header when in TUN mode, so we need to modify the read/
 // writes to handle those first four bytes
 
+func defaultTUNParameters() tunDefaultParameters {
+	return tunDefaultParameters{
+		maxMTU: 16384,
+	}
+}
+
 // Warning! When porting this to other BSDs, the tuninfo struct can appear with
 // the fields in a different order, and the consts below might also have
 // different values
@@ -80,7 +86,7 @@ func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int)
 		panic(err)
 	}
 	tun.iface = iface
-	tun.mtu = mtu //1280 // Lets default to the smallest thing allowed for now
+	tun.mtu = getMTUFromMax(mtu)
 	return tun.setupAddress(addr)
 }
 
diff --git a/src/yggdrasil/tun_other.go b/src/yggdrasil/tun_other.go
index ec56408..5e33fee 100644
--- a/src/yggdrasil/tun_other.go
+++ b/src/yggdrasil/tun_other.go
@@ -7,6 +7,12 @@ import water "github.com/neilalexander/water"
 // This is to catch unsupported platforms
 // If your platform supports tun devices, you could try configuring it manually
 
+func defaultTUNParameters() tunDefaultParameters {
+	return tunDefaultParameters{
+		maxMTU: 65535,
+	}
+}
+
 func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int) error {
 	var config water.Config
 	if iftapmode {
@@ -19,7 +25,7 @@ func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int)
 		panic(err)
 	}
 	tun.iface = iface
-	tun.mtu = mtu //1280 // Lets default to the smallest thing allowed for now
+	tun.mtu = getMTUFromMax(mtu)
 	return tun.setupAddress(addr)
 }
 
diff --git a/src/yggdrasil/tun_windows.go b/src/yggdrasil/tun_windows.go
index a2108fe..9e8dda4 100644
--- a/src/yggdrasil/tun_windows.go
+++ b/src/yggdrasil/tun_windows.go
@@ -7,6 +7,12 @@ import "fmt"
 
 // This is to catch Windows platforms
 
+func defaultTUNParameters() tunDefaultParameters {
+	return tunDefaultParameters{
+		maxMTU: 65535,
+	}
+}
+
 func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int) error {
 	if !iftapmode {
 		tun.core.log.Printf("TUN mode is not supported on this platform, defaulting to TAP")
@@ -41,7 +47,7 @@ func (tun *tunDevice) setup(ifname string, iftapmode bool, addr string, mtu int)
 		panic(err)
 	}
 	tun.iface = iface
-	tun.mtu = mtu
+	tun.mtu = getMTUFromMax(mtu)
 	err = tun.setupMTU(tun.mtu)
 	if err != nil {
 		panic(err)